Flight vehicles including scribed frangible seals and methods for the manufacture thereof

ABSTRACT

Embodiments of a flight vehicle including a scribed frangible seal are provided, as are embodiments of a scribed frangible seal and a method for equipping a flight vehicle with a scribed frangible seal. In one embodiment, the flight vehicle includes a vehicle body having a deployment opening therein, and a deployable element residing in a stowed position within the vehicle body and movable into a deployed position. At least a potion of the deployable element passes through the deployment opening when moving from the stowed position into the deployed position. The flight vehicle further includes a scribed frangible seal, which is sealingly disposed over the deployment opening and which is positioned so as to be contacted by the deployable element during deployment thereof. The scribed frangible seal fractures along at least one scribe line when contacted by the deployable element to permit movement of the deployable element from the stowed position to the deployed position.

TECHNICAL FIELD

The following disclosure relates generally to flight vehicles and, moreparticularly, to embodiments of guided munitions and other flightvehicles including scribed frangible seals.

BACKGROUND

Certain guided munitions are equipped with a plurality offorward-mounted wings or canards, which are hingedly mounted to aforward section of the munition body (e.g., the guidance section shell)for inflight movement from a stowed position to a deployed position. Inthe stowed position, the canards are recessed within the munition bodyto impart the guided munition with a streamlined envelope well-suitedfor loading into a launch tube or similar enclosure. During deployment,the canards rotate about a hinge pin, through longitudinal slotsprovided in the munition body, and into a deployed position wherein thecanards project radially outward from the munition body to provideaerodynamic guidance during flight. The outward rotation of the canardsis typically driven by specialized springs housed within the munitionbody in combination with centrifugal forces, which act on the rollingmunition during flight. Canards are, of course, only one example ofdeployable elements that may be carried by a guided munition anddeployed during flight. Examples of other deployable elements include,but are not limited to, other types of flight guidance structures, airturbines, and seeker heads.

If not adequately sealed, canard slots and other deployment openings inthe munition body may permit the ingress of environmental contaminants,such as water droplets, ice, dirt, sand, and other debris. If permittedto accumulate within the guided munition, such contaminants canpotentially interfere with the operation of the munition's internalcomponents, such as the control actuation system utilized to manipulatethe canards during flight. Environmental seals have been developed thatcan seal canard slots and other openings in the munition fuselage toprevent or minimize the ingress of contaminants. Conventionalenvironmental seals are, however, limited in several regards.Conventional environmental seals are typically incapable of maintainingsealing properties when repeatedly exposed to extreme thermal andpressure loading conditions. As a result, conventionally-knownenvironmental seals are typically unsuitable for usage in conjunctionwith guided munitions carried by multi-tube launchers and repeatedlyexposed to rocket motor exhaust during the launch of neighboringmunitions. Similarly, conventionally-known environmental seals may beunsuitable for usage with guided munitions exposed high thermal loadsdue to aerodynamic heating during supersonic flight. As a furtherlimitation, conventionally-known environmental seals typically requirededicated actuators (e.g., electromechanical or pyrotechnic devices) tojettison or otherwise displace the seals immediately prior to canarddeployment. Such dedicated seal actuators add undesired cost, weight,and bulk to guided munition. In addition, the usage of such dedicatedseal actuators may be precluded by spatial limitations in the case oflaser-guided rockets and other small form factor munitions.

There thus exists an ongoing need to provide embodiments of anenvironmental seal suitable for sealing a deployment opening in the bodyof a guided munition or other flight vehicle that overcomes many, if notall, of the above-noted limitations. In particular, it would bedesirable to provide an environmental seal through which a deployableelement (e.g., a canard) may deploy in a reliable and lower energymanner without requiring a dedicated seal actuator. Ideally, embodimentsof such an environmental seal would be capable of maintaining structuralintegrity and sealing properties through repeated exposure to relativelyharsh thermal and pressure loading conditions. It would also bedesirable for such an environmental seal to be relatively inexpensive toproduce, to be amenable to automated manufacture, to be compact andlightweight, to have a relatively low water vapor permeability, and toproduce little to no sizable debris upon deployment. Lastly, it would bedesirable to provide embodiments of a flight vehicle equipped with oneor more environmental seals of the type described above, and to providemethods for equipping flight vehicles with environmental seals. Otherdesirable features and characteristics of the present invention willbecome apparent from the subsequent Detailed Description and theappended Claims, taken in conjunction with the accompanying Drawings andthis Background.

BRIEF SUMMARY

Embodiments of a flight vehicle are provided. In one embodiment, theflight vehicle includes a vehicle body having an opening therein; adeployable element, which resides in a stowed position within thevehicle body and which is movable into a deployed position; and ascribed frangible seal. At least a potion of the deployable elementpasses through the opening when moving from the stowed position into thedeployed position. The flight vehicle further includes a scribedfrangible seal, which is sealingly disposed over the deployment openingand which is positioned so as to be contacted by the deployable elementduring deployment thereof. The scribed frangible seal fractures along atleast one scribe line when contacted by the deployable element to permitmovement of the deployable element from the stowed position to thedeployed position.

Embodiments of a scribed frangible seal are further provided for sealinga deployment opening through which a deployable element deploys. In oneembodiment, the scribed frangible seal includes a ceramic substrate andat least one laser scribe line, which is formed in a surface of theceramic substrate and which impart the ceramic substrate with apredetermined rupture strength. The ceramic substrate fractures alongthe at least one laser scribe lines when contacted by the deployableelement during deployment thereof.

Embodiments of a method for equipping a flight vehicle with a scribedfrangible seal are still further provided. The flight vehicle includes avehicle body configured to house a deployable element when in a stowedposition. The vehicle body has a deployment opening therein throughwhich at least a portion of the deployable element passes when movingfrom the stowed position into a deployed position. In one embodiment,the method includes the steps of obtaining a scribed frangible seal,positioning the scribed frangible seal over the deployment opening inthe vehicle body at a location at which the scribed frangible seal willbe contacted by the deployable element during deployment thereof, andbonding the scribed frangible seal to the vehicle body to seal thedeployment opening.

BRIEF DESCRIPTION OF THE DRAWINGS

At least one example of the present invention will hereinafter bedescribed in conjunction with the following figures, wherein likenumerals denote like elements, and:

FIG. 1 is an isometric view of a plurality of guided munitions carriedby an exemplary multi-tube launcher;

FIG. 2 is an isometric view of an exemplary guided munition after launchfrom the multi-tube launcher shown in FIG. 1 and equipped with aplurality of canards, which deploy through a plurality of canard slotsformed in the munition body;

FIG. 3 is an isometric view illustrating a canard in a stowed positionand a scribed frangible seal suitable for creating an environmental sealover one of the canard slots shown in FIG. 2 and illustrated inaccordance with an exemplary embodiment of the present invention;

FIGS. 4 and 5 are top-down and cross-sectional views, respectively,illustrating a portion of a laser scribe line formed in the substrate ofthe scribed frangible seal shown in FIG. 3;

FIGS. 6 and 7 are isometric views of a portion of the munition bodyshown in FIG. 2 prior to and after, respectively, the installation ofplurality of scribed frangible seals over the canard slots provided inthe munition body;

FIG. 8 is a cross-sectional view of a canard in a stowed position andthe scribed frangible seal shown in FIG. 3 illustrating a firstexemplary manner in which the scribed frangible seal may be adhesivelyattached to the munition body utilizing a flexible edge bond;

FIG. 9 is a cross-sectional view of the canard and scribed frangibleseal shown in FIG. 8 during deployment of canard through the scribedfrangible seal and the fracture of the scribed frangible seal into twolongitudinally-extending pieces, which rotate outward from the munitionbody about the flexible edge bond to permit passage of the canard;

FIG. 10 is a cross-sectional view of a canard in a stowed position andthe scribed frangible seal shown in FIG. 3 illustrating a secondexemplary manner in which the scribed frangible seal may be adhesivelyattached to the munition body utilizing a face bond; and

FIG. 11 is a flowchart illustrating an exemplary method for equipping aguided munition or other flight vehicle with a scribed frangible seal.

DETAILED DESCRIPTION

The following Detailed Description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by any theorypresented in the preceding Background or the following DetailedDescription. As appearing herein, the term “flight vehicle” is definedto encompass munitions, sub-munitions, munition-mountable devices (e.g.,precision guidance kits), Unmanned Aerial Vehicles, exoatmosphericvehicles, spacecraft, and other airborne and space-borne platforms oftype which carry at least one deployable device or structure. As furtherappearing herein, the term “scribe line” is utilized to denote an areaof reduced thickness formed in a frangible, rigid substrate to promotefracture of the substrate when contacted by a deployable element, suchas a deployable flight control surface, during deployment thereof.Unless otherwise specified, the area of reduced thickness is not limitedto any particular shape or pattern and may assume the form of, forexample, a continuous (unbroken) line or discontinuous (broken, dashed,or dotted) line, whether having a linear (straight) or non-lineargeometry.

The following describes several exemplary embodiments of a scribedfrangible seal, such as a laser scribed ceramic seal, that providesmultiple advantages over conventionally-known environmental seals.Amongst other advantages, embodiments of the scribed frangible sealdescribed herein are able maintain structural integrity and sealingproperties through repeated exposure to highly elevated thermal andpressure loading conditions. In addition, embodiments of the scribedfrangible seal are compact, lightweight, and enable reliable deploymentof a deployable element (e.g., a canard) at a desired time of deploymentwithout the assistance of a dedicated seal actuator. For these reasons,embodiments of the scribed frangible seal are especially well-suited forusage in conjunction with small form factor guided munitions and/ormunitions repeatedly exposed to high thermal and pressure loadingconditions prior to munition launch. To further emphasize this point,the following describes embodiments of the scribed frangible seal inconjunction with a particular type of guided munition carried by aparticular type of launch platform, namely, a laser-guided rocketcarried by a multi-tube launcher. This notwithstanding, it is emphasizedthat embodiments of the scribed frangible seal can be deployed onboardother guided munitions and launch platforms including, for example, aguided munition carried by the wing of a supersonic aircraft.Additionally, embodiments of the scribed frangible seal described hereincan be utilized to seal openings in the bodies or fuselages of flightvehicles other than guided munitions including, but are not limited to,satellite, exoatmospheric vehicles, and Unmanned Aerial Vehicles.Similarly, embodiments of the scribed frangible seal described hereincan be utilized to seal deployment openings in munition systemsgenerally, such as an opening provided through a launch canister orother launch enclosure through which a guided munition is launched.Lastly, while described below in conjunction with a particular type ofdeployment opening (i.e., a plurality of canard slots) through which aparticular type of flight guidance structure (i.e., a plurality ofcanards) deploys, it is further emphasized that embodiments of thescribed frangible seal can be utilized to sealingly enclose any openingprovided in the body or fuselage of a flight vehicle through which adeployable element (e.g., a flight guidance structure, an air turbine, aseeker head, or the like) deploys.

FIG. 1 is an isometric view of an exemplary multi-tube launcher 12carried by an arm 14 of a rotary-wing aircraft 16. Multi-tube launcher12 includes a plurality of launch tube openings 18 into which a numberof guided munitions 20 are loaded such that a forward end of eachmunition 20 extends beyond the leading face or bulkhead of launcher 12.Guided munitions 20 are sequentially launched or fired from multi-tubelauncher 12 on an as-needed basis. To launch a particular guidedmunition 20 from launcher 12, an ignition charge is triggered toinitiate controlled combustion of a solid propellant held within themunition's rocket motor section and thereby generate exhaust gases,which flow through the munition's rocket motor nozzle to produce forwardthrust. As the aft end of the munition clears the mouth of its launchtube opening, the hot combustive gases exhausted by the munition impingeupon the bulkhead of multi-tube launcher 12, spread radially outward,and flow over the exposed forward ends of the munitions remaining withinlauncher 12. The exposed forward ends of the munitions remaining withinmulti-tube launcher 12 are thus enveloped in a plume of rocket motorexhaust each time a neighboring munition is launched from launcher 12. Agiven munition carrier by launcher 12 can consequently be subjected tohighly elevated temperatures and localized pressures several timesbefore the guided munition is, itself, launched; e.g., in theillustrated embodiment wherein launcher 12 assumes the form of anineteen-tube launcher, the forward end of the last-launched munitionmay be enveloped in rocket motor exhaust eighteen times prior to usageand excluding reloading of launcher 12.

FIG. 2 is an isometric view of a guided munition 20 after launch frommulti-tube launcher 12 (FIG. 1) and illustrated in accordance with anexemplary embodiment of the present invention. In this particularexample, guided munition 20 assumes the form of a laser-guided rockethaving a rocket motor section 22, a warhead section 24, and a guidancesection 26. Rocket motor section 22 includes a tubular casing 28containing a solid propellant or grain (not shown), a rocket motornozzle 30 mounted to the aft end of casing 28, and a plurality of tailfins 32 circumferentially spaced about the aft end of casing 28proximate nozzle 30. Warhead section 24 includes a tubular shell 34containing one or more warheads (also not shown). Guidance section 26includes a tubular shell 36, a seeker 38 mounted to the forward end ofshell 36, and a plurality of forward-mounted wings or canards 40.Canards 40 are hingedly mounted to a mid-section of shell 36 such thateach canard 40 is movable from a stowed position to the deployedposition shown in FIG. 2 at a desired time of deployment. Collectively,casing 28 of rocket motor section 22, shell 34 of warhead section 24,and shell 36 of guidance section 26 form the body of guided munition 20.Although hidden from view in FIG. 2, guidance section 26 furtherincludes at least one fuse; a control actuation system for inflightmanipulation of canards 40; and an onboard navigational computeroperably coupled to the fuse, the control actuation system, and seeker38. During flight, seeker 38 provides the onboard navigational computerwith signals indicative of target location based upon, for example,registered laser pulse energy reflected from a designated target andemitted from a laser designator. Navigational computer then determinesfrom these signals the manner in which the rotational position canards40 should be manipulated by the control actuation system to guidemunition 20 to its designated target in a highly accurate manner.

A plurality of longitudinal openings or slots 42 is provided throughguidance section shell 36 adjacent the location at which canards 40 arehingedly coupled to shell 36. As are canards 40, slots 42 arecircumferentially spaced around a mid-section of guidance section shell36. Canard slots 42 each assume the form of an elongated opening oraperture formed through the annular sidewall of guidance section shell36 and extend in a direction substantially parallel with thelongitudinal axis of guided munition 20. In the stowed position, canards40 reside within shell 36 to provide physical protection and to impartmunition 20 with a streamlined profile well-suited for loading intomulti-tube launcher 12 (FIG. 1) or a similar launch platform. Asindicated in FIG. 2 by arrows 44, canards 40 rotate outward from thebody of munition 20, through canard slots 42, and into their deployedpositions at the desired time of deployment, which will typically beduring launch or during the early stages of munition flight. When fullydeployed, canards 40 project radially outward from guidance sectionshell 36 to provide aerodynamic guidance during munition flight, aspreviously described. The outward rotation of canards 40 is driven byspecialized springs housed within guided munition 20 (not shown) incombination with centrifugal forces, which act on canards 40 as guidedmunition 20 spins or rolls rapidly during flight.

It is desirable to seal canard slots 42 to prevent the ingress ofenvironmental contaminants (e.g., water droplets, ice, dirt, sand, andother debris) that could potentially interfere with the internaloperation of guided munition 20 and decrease munition reliability. Whileenvironmental seals have been developed for usage in conjunction withcertain guided munitions, conventionally-known environmental seals aregenerally unsuitable for usage in conjunction with guided munition 20and similar guided munitions for at least two reasons. First, guidedmunition 20 has a relatively compact form factor, when viewed along itslongitudinal axis in a fore-aft direction; e.g., the maximum outerdiameter of the body of munition 20 may be approximately 70 millimeters(2.75 inches). Insufficient space may consequently be provided toaccommodate the dedicated actuators (e.g., electromechanical orpyrotechnic devices) typically required to jettison or other removeconventionally-known environmental seals prior to canard deployment.Second, conventionally-known environmental seals are generally unable tomaintain adequate sealing properties through repeated exposure to harshthermal and pressure loading conditions. As a result,conventionally-known environmental seals are typically unsuitable forusage in conjunction with a multi-tube launcher (e.g., launcher 12 shownin FIG. 1) wherein any externally-exposed structure located at themunition's forward end, including any environmental seals positionedover slots 42, may be directly and repeatedly contacted by rocket motorexhaust during the launch of neighboring munitions (note that canardsslots 42 and any environmental seals covering slots 42 are not shown inFIG. 1 for clarity). The following describes several exemplaryembodiments of a scribed frangible seals useful for forming anenvironmental seal over a canard slot (or other deployment opening)provided in the body of a guided munition (or other flight vehicle) thatis relatively compact, that does require the provision of a dedicatedseal actuator, and that is capable of maintaining sealing propertiesthrough repeated exposure to highly elevated thermal and pressureloading conditions.

FIG. 3 is an isometric view of a canard 40 and a scribed frangible seal46 suitable for sealing or enclosing one of canard slots 42 formed inshell 36 of guided munition 20 (shown in FIG. 2) in accordance with anexemplary embodiment of the present invention. Scribed frangible seal 46includes a rigid substrate 48 having a plurality of scribe lines 56formed therein. Rigid substrate 48 is preferably fabricated as a singleor unitary piece, although the possibility that rigid substrate 48 maybe fabricated from multiple pieces or components is by no meansexcluded. As shown in FIG. 3, rigid substrate 48 will typically assumethe form of a relatively thin, plate-like body; however, it will beunderstood that the particular geometry and dimensions of substrate 48will vary in further embodiments depending upon the particular shape andsize of the munition opening sealed by scribed frangible seal 46. In theillustrated example wherein scribed frangible seal 46 is utilized tosealingly enclose an elongated canard slot, rigid substrate 48 isfabricated to have an elongated, generally rectangular geometry suitablefor covering the entirety of slot 42 when substrate 48 is bonded orotherwise attached to guidance section shell 36, as described more fullybelow in conjunction with FIGS. 6-9. The thickness of rigid substrate 48will generally be determined by space constraints and the desiredrupture strength of scribed frangible seal 46; however, by way ofnon-limiting example, substrate 48 may have a thickness betweenapproximately 0.010 and 0.030 inch.

Substrate 48 may be fabricated from various different materials,depending upon desired rupture strength, temperature tolerances, andsimilar considerations. Candidate materials include, but are not limitedto, plastics, glasses, ceramics, and silicon-containing materials. Theseexamples notwithstanding, substrate 48 is preferably fabricated from aceramic material. As appearing herein, a “ceramic material” or a“ceramic” is defined as an inorganic and non-metallic material, whethercrystalline or amorphous. Advantageously, and in contrast to organicmaterials, ceramics are able to withstand highly elevated temperatureswith little to no structural degradation and are consequentlywell-suited for usage when seal 46 is subjected to extreme temperaturesdue to, for example, repeated exposure to rocket motor exhaust.Additionally, ceramics are relatively brittle when placed under tensionand can thus be designed, by strategic positioning of scribe lines 56,to fracture when rigid substrate 48 is subjected to a relatively modestinternal loading force, as will be described below. As a furtheradvantage, ceramic materials also typically have relatively low watervapor transmission rates to support desiccant sizing of substrate 48. Anon-exhaustive list of ceramics suitable for the fabrication ofsubstrate 48 includes alumina, zirconia, silicon carbide, berylliumoxide, and aluminum nitride. Of the foregoing list, aluminum oxide oralumina (Al₂O₃) is generally preferred in view of its relatively lowcost and widespread commercial availability.

Scribe lines 56 are advantageously formed in at least the outer face 50of substrate 48; that is, the outer major surface of substrate 48residing substantially opposite canard 40 (or other deployable element)when in the stowed position. Formation of scribe lines 56 in theoutermost face 50 of substrate 48 is particularly advantageous inembodiments wherein substrate 48 is fabricated from a ceramic or othermaterial prone to failure under tension; in such embodiments,application of a relatively modest force to the inner face of substrate48 by canard 40 (or a like deployable element) will place scribed outerface 50 in tension and readily initiate fracture of substrate 48. Thus,by forming substrate 48 from a ceramic and by forming scribe lines 56 inouter face 50, scribed frangible seal 46 can be designed to fracture orfail with minimal internal loading and, therefore, with the aid of a lowforce/energy deployment spring acting on substrate 48 through canard 40.Externally-applied forces, by comparison, will tend to place scribedouter face 50 in compression and therefore be less likely to result inthe inadvertent or premature fracture of substrate 48. The inner face ofrigid substrate 54, which resides adjacent canard 40 in the stowedstate, may be left unscribed to further decrease the likelihood of theinadvertent fracture of substrate 48 due to externally-applied forces.Alternatively, scribe lines may be formed in the inner face of substrate48 in addition to outer face 50 to minimize the rupture threshold ofscribed frangible seal 46.

Scribe lines 56 can be formed by any suitable mechanical process whereinmaterial is removed from one or more surfaces of rigid substrate 48utilizing a cutting tool, such as a diamond saw. Alternatively, scribelines 56 can be formed by an additive process wherein substrate 48 isfabricated to inherently include regions of reduced thickness by, forexample, a casting process, a molding process, or through the usage of arapid prototyping technique, such as stereolithography (also commonlyreferred to as “three dimensional printing,” “photo-solidification,” or“optical printing”). These examples notwithstanding, scribes lines 56are preferably formed utilizing a laser scribing process. The industrialviability and capabilities of laser scribing processes have beenwell-demonstrated within the semiconductor industry wherein suchprocesses are utilized during singulation of wafers into individual die(commonly referred to as “dicing”). During laser scribing, a laser iscontrolled to impinge upon selected areas of substrate 48 and removematerial therefrom. The laser energy may be pulsed as the laser passesover the outer surface of substrate 48 such that each scribe line 56 isformed as a series of perforations or blind holes. To further exemplifythis point, FIGS. 4 and 5 are top-down and cross-sectional views,respectively, illustrating a segment of a laser scribe line 56(a) formedin a portion of substrate 48. As can be seen in FIGS. 4 and 5, laserscribe line 56(a) is generally defined by a series of blind holes 58,which are formed in outer face 50 of substrate 48 and which extendtoward, but do not penetrate, inner face 60 of substrate 48. Notably,the laser scribing process parameters (e.g., laser pulse intensity,duration, sweep, etc.) can be manipulated, as appropriate, to adjust theaverage pitch or spacing (identified as “S” in FIG. 5), width,(identified as “W” in FIG. 5), and depth (identified as “D” in FIG. 5)of blind holes 58 and thereby impart rigid substrate 48 with a targetedrupture strength in a highly controllable manner. Laser scribing canalso be utilized in combination with mechanical breaking to separatesubstrate 48 from a larger ceramic sheet, as described more fully belowin conjunction with FIG. 11.

The dimensions, orientation, location, and pattern of scribe lines 56may vary amongst different embodiments of frangible seal 46. In certainembodiments, scribe lines 56 may form a cross-hatched, grid, or latticepattern across outer face 50 of rigid substrate 48. In preferredembodiments, scribe lines 56 extend from an aft portion of substrate 48to a forward portion thereof in a generally longitudinal direction. Inthe exemplary embodiment illustrated in FIG. 3, specifically, fivesubstantially parallel scribe lines 56 are formed in a central portionof outer face 50 and extend from an aft end portion of substrate 48 tothe forward end portion thereof; stated differently, scribe lines 56 areformed proximate and are substantially parallel to the centerline offrangible seal 46. To optimize energy propagation during substratefracture, scribe lines 56 are preferably each formed have asubstantially linear or straight geometry; however, various othergeometries are also possible. Regardless of the particular form assumedthereby, scribe lines 56 are preferably produced in a region ofsubstrate 48 substantially opposite the location at which canard 40impacts substrate 48 during deployment. The formation multiple scribelines helps to ensure canard impact within close proximity of at leastone scribe line and thus compensates for variation that may occur inimpact location within acceptable manufacturing tolerances. By forming aplurality of substantially parallel scribe lines 56 across a centralportion of rigid substrate 48 in the manner shown in FIG. 5, a preferredfailure mode can be reliably achieved wherein substrate 48 fractures(and thus energy propagates) along a single, substantially linear,longitudinally-extending fault line, which extends the length of rigidsubstrate 48. In the illustrated example, scribe lines 56 extend acrossthe entire length of rigid substrate 48 and, thus, from the forward edgeof substrate 48 to the aft edge thereof. In further embodiments, scribelines 56 may terminate prior to reaching the outermost edges ofsubstrate 48. In still further embodiments, and by way of example only,scribe lines 56 may converge to notches or cut-outs formed in opposingends of rigid substrate 48 to further promote fracture of substrate 48along a substantially linear, longitudinally-extending fault line.

FIGS. 6 and 7 are isometric views of guidance section shell 36 prior toand after the installation of scribed frangible seals 46 over canardslots 42, respectively. As shown most clearly in FIG. 6, longitudinaldepressions 53 are formed in the external surface of shell 36 aroundcanard slots 42 such that each canard slot 42 is surrounded orcircumscribed by an individual depression 53. Scribed frangible seals 46are matingly installed within depressions 53. Depressions 53 may eachhave a length and width slightly greater than the length and width ofseals 46, providing that a circumferential clearance is provided aroundeach seal 46 for the application of a high temperature adhesive. Thedepth of depressions 53 is preferably equivalent to or slightly greaterthan the thickness of seals 46. When installed within depressions 53,scribed frangible seals 46 cooperate with guidance section shell 36 toform an aerodynamically streamlined structure having a substantiallyuninterrupted outer annular surface. Furthermore, when installed withindepressions 53, the outer surfaces or faces of seals 46 may besubstantially flush with or slightly recessed with respect to the outersurface of guidance section shell 36.

FIG. 8 is a cross-sectional view taken through a scribed frangible seal46 and a portion of guidance section shell 36 illustrating one manner inwhich seal 46 may be adhesively bonded to shell 36 and, specifically, tothe surfaces of shell 36 defining depression 53. It can be seen in FIG.8 that a central longitudinal portion of inner face 60 of rigidsubstrate 48 is exposed through canard slot 42, while the outerlongitudinal portions of inner face 60 are supported by the floor 62 ofdepression 53. Such a supportive arrangement further decreases thelikelihood of the inadvertent or premature fracture of seal 46 due toexternally-applied forces. It can also be seen in FIG. 8 that scribelines 56 are formed in the outer face 50 substantially opposite canard40 and, in particular, substantially opposite the location at whichcanard 40 will contact rigid substrate 48 during deployment. A hightemperature adhesive 64 is applied around seal 46 such that the outercircumferential edge 52 of substrate 48 is bonded to the inner sidewallsof depression 53. The chosen adhesive is preferably able to remainflexible for an extended time period over the operational temperaturerange of guided munition 20 (FIG. 2). In addition, the chosen adhesivepreferably has sufficient flexibility (e.g., compressibility and/orelasticity) to accommodate relative movement between the outer edges ofrigid substrate 48 and the inner circumferential surfaces of shell 36defining depression 53 that may occur during heating due to differencesin coefficients of thermal expansion. In one embodiment, a hightemperature silicone adhesive is utilized, such as RTV88 siliconeadhesive commercially available from Momentive Performance Materials,Incorporated, currently headquartered in Columbus, Ohio. While abuttingfloor 62 of depression 53 when seal 46 is positioned therein, inner face60 of substrate 48 is preferably not bonded to guidance section shell 36such that, when seal 46 fractures into at least two pieces, the twopieces can readily rotate or hinge outward to permit the passage ofcanard 40, as described below in conjunction with FIG. 9.

FIG. 9 is a cross-sectional view illustrating scribed frangible seal 46during deployment of a canard 40. As indicated in FIG. 9 by arrow 66,canard 40 has contacted and exerted sufficient force on substrate 48 tocause seal 46 fracture along a longitudinal fault line 68 into twoopposing sections or pieces 46(a) and 46(b). As further indicated inFIG. 9 by arrows 70, the inner edges of seal pieces 46(a) and 46(b)rotate outward from guided munition shell 36 about the locations atwhich pieces 46(a) and 46(b) are flexibly bonded to shell 36,respectively, to accommodate the passage of canard 40. As this occurs,any flexible adhesive present at the opposing aft and forward ends ofrigid substrate 48 tears to allow the outward divergent rotation of sealpieces 46(a) and 46(b). Such a flexible edge bond provides a relativelylong moment arm to assists with centerline fracture of rigid substrate48 along longitudinally-extending scribe lines 56. In so doing, theflexible edge bond allows canard penetration through seal 46 in responseto a relatively modest force applied to inner face 60 of substrate 48substantially opposite scribe lines 56 as may be provided by arelatively weak spring force (e.g., a spring force less thanapproximately 18 pound-force, as applied to substrate 48) and,therefore, without provision of a dedicated seal actuator (e.g., anelectromechanical or pyrotechnic device) of the type utilized tojettison or displace conventionally-known environmental seals.Furthermore, as seal pieces 46(a) and 46(b) remain attached to themunition body, little to no debris is produced by deployment of canard40 through scribed frangible seal 46.

In further embodiments of scribed frangible seal 46, a face bond may beemployed in addition to, or in lieu, of a flexible edge bond; that is,inner face 60 of substrate 48 may be bonded to floor 62 of depression53, as shown in FIG. 10 at 72. In general, when a face bond is utilizedin addition to or in lieu of a flexible edge bond, substrate 48 willfracture along multiple scribe lines and require a greater deploy forceto initiate substrate fracture and allow the passage of a canard orother deployable element therethrough. However, while requiring theapplication of a larger deployment force, a face bond provides severaladvantages. For example, a face bond will tend to produce a more robustenvironmental seal between substrate 48 and guidance section shell 36.In addition, the lateral stand-off provided by a face bond assists withpositioning substrate 48 and facilitates bonding during the assemblyprocess. Thus, in embodiments wherein seal 46 is utilized in conjunctionwith larger form factor munitions capable of accommodating larger deploysprings, a face bond may be utilized, possibly in conjunction withscribe lines formed in opposing faces of substrate 48.

FIG. 11 is a flowchart illustrating an exemplary method 80 for equippinga guided munition with a scribed frangible seal, such as seal 46described above in conjunction with FIGS. 3-10. Exemplary method 80commences with the provision of a substrate, such as substrate 48 shownin FIGS. 3-10 (STEP 82). To commence method 80, a ceramic sheet mayfirst be laser scribed and then broken, either mechanically or manually,into a plurality of individual substrates (STEPS 82(b) and 82(b)). Theceramic sheet may itself be produced utilizing fabrication byroll-compaction and sintering of a slurry containing ceramic particles.Scribes lines are then formed in at least one surface of the substrateutilizing, for example, a laser scribing process (STEP 82(c)). Morespecifically, as described above in conjunction with FIG. 3, a pluralityof substantially parallel laser scribe lines may be formed in the outersurface of substrate such that each scribe line extends in asubstantially longitudinal direction from an aft portion of thesubstrate to a forward portion thereof. The outer face of the substratemay or may not be polished or lapped after laser scribing. Next (STEP84), the laser scribed seal is positioned over a deployment opening(e.g., a canard slot) provided in the body of a flight vehicle (e.g., aguided munition) such that at least one scribed surface of the sealresides substantially opposite the location at which a canard or otherdeployable element is housed within the flight vehicle body. Asdescribed above in conjunction with FIGS. 6 and 7, the laser scribedseal may be matingly positioned within a depression or recess providedin the munition shell. To complete method 80, the laser scribed seal maythen be adhesively bonded to the flight vehicle body (e.g., the munitionshell) utilizing a suitable bonding agent, such a high temperaturesilicone adhesive of the type described above (STEP 86). One or morecleaning agents or priming agents may also be applied prior toapplication of the selected bonding agent. A flexible edge bond of thetype described above in conjunction with FIGS. 8 and 9 is advantageouslyemployed to attach the substrate to the vehicle body. To minimizerequired human touch during the installation process, application of thebonding agent and primer, if utilized, may advantageously be performedutilizing an automated robot. After application of the bonding agent, acuring process may then be performed according to a pre-establishedcuring scheduled to set the bonding agent and thereby form a robustenvironmental seal (e.g., a near-hermetic seal) between the substrateand the munition body. Lastly, to ensure adequate sealing of thedeployment opening, inspection may be performed either visually orutilizing a suitable inspection tool or technique, such as a pressuretest.

The foregoing has thus provided multiple exemplary embodiments of anscribed frangible seal suitable for sealing a deployment opening in thebody of a flight vehicle (e.g., a canard slot or other opening in theshell of a guided munition) through which a deployable element (e.g., acanard) can deploy without the usage of a dedicated seal actuator.Embodiments of the above-described environmental seal are able to remainstructurally intact and to maintain adequate sealing properties throughrepeated exposure to extreme thermal and pressure loading conditions andare consequently well-suited for usage within guided munitions carriedby multi-tube launchers and supersonic aircraft. Embodiments of theabove-described scribed frangible seal are relatively inexpensive toproduce, are amenable to automated manufacture, are compact andlightweight, produce no sizable debris upon deployment, have arelatively low water vapor permeability, and allow deployment inreliable and repeatable manner. The foregoing has also providedembodiments of a guided munition or other flight vehicle equipped withsuch a scribed frangible seal, as well as embodiments of a method forequipping a flight vehicle with such a scribed frangible seal.

While described above primarily in the context of a guided munition,embodiments of the scribed frangible seal disclosed herein can beutilized to seal deployment openings in munition systems generallyincluding, for example, containerized munition systems. For example,embodiments of the scribed frangible seal can be utilized to seal adeployment opening provided through a launch canister or other launchenclosure from which a containerized guided munition is launched. Inthis case, the scribe frangible seal may assume the form of a lid, whichis sealingly positioned over the launch canister's open end and whichfractures when the guided munition is launched from the launch canister,due either to contact with the nose of the guided munition (thedeployable element) during munition fly-out.

While at least one exemplary embodiment has been presented in theforegoing Detailed Description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the foregoing Detailed Description willprovide those skilled in the art with a convenient road map forimplementing an exemplary embodiment of the invention. It beingunderstood that various changes may be made in the function andarrangement of elements described in an exemplary embodiment withoutdeparting from the scope of the invention as set-forth in the appendedClaims.

What is claimed is:
 1. A flight vehicle, comprising: a vehicle bodyhaving a deployment opening therein; a deployable element residing in astowed position within the vehicle body and movable into a deployedposition, at least a portion of the deployable element passing throughthe deployment opening when moving from the stowed position into thedeployed position; and a scribed frangible seal sealingly disposed overthe deployment opening and positioned so as to be contacted by thedeployable element during deployment thereof, the scribed frangible sealfracturing along at least one scribe line when contacted by thedeployable element to permit movement of the deployable element from thestowed position to the deployed position.
 2. A flight vehicle accordingto claim 1 wherein the scribed frangible seal comprises a rigidsubstrate bonded to the vehicle body.
 3. A flight vehicle according toclaim 2 wherein the scribed frangible seal further comprises a pluralityof scribe lines formed in at least one surface of the rigid substrate.4. A flight vehicle according to claim 3 wherein the plurality of scribelines comprises a plurality of scribe lines formed in an outer face ofthe rigid substrate substantially opposite the location at which thedeployable element contacts the rigid substrate during deployment.
 5. Aflight vehicle according to claim 3 wherein the plurality of scribelines extends in a substantially longitudinal direction from a forwardportion of the rigid substrate to an aft portion thereof.
 6. A flightvehicle according to claim 5 wherein the plurality of scribe linescomprises a plurality of substantially parallel scribe lines eachextending in a direction substantially parallel with the longitudinalaxis of the flight vehicle.
 7. A flight vehicle according to claim 3wherein the plurality of scribe lines comprises a plurality of laserscribe lines formed in an outer face of the rigid substrate.
 8. A flightvehicle according to claim 7 wherein each of the plurality of laserscribe lines comprises a series of blind holes formed in the outer faceof the rigid substrate.
 9. A flight vehicle according to claim 7 whereinthe rigid substrate is fabricated from a ceramic.
 10. A flight vehicleaccording to claim 9 wherein the rigid substrate is fabricated fromalumina.
 11. A flight vehicle according to claim 3 further comprising adepression formed in the vehicle body and at least partially surroundingthe deployment opening, at least a portion of the rigid substratedisposed within the depression.
 12. A flight vehicle according to claim11 wherein the depression is formed in an external surface of thevehicle body, and wherein the rigid substrate is matingly receivedwithin the depression in its substantial entirety.
 13. A flight vehicleaccording to claim 11 further comprising a flexible edge bond joining atleast a portion of the circumferential edge of the rigid substrate to atleast one surface of the vehicle body defining the depression.
 14. Aflight vehicle according to claim 13 wherein the rigid body fracturesinto at least two longitudinally-extending pieces when contacted by thedeployable during deployment thereof, and wherein the twolongitudinally-extending pieces each rotate about the flexible edge bondto permit movement of the deployable element from the stowed position tothe deployed position.
 15. A flight vehicle according to claim 1 whereinthe flight vehicle comprises a guided munition, wherein the vehicle bodycomprises a munition body, wherein the deployable element comprises acanard, and wherein the deployment opening comprises a canard slot. 16.A scribed frangible seal for sealing a deployment opening through whicha deployable element deploys, the scribed frangible seal comprising: aceramic substrate; and at least one laser scribe line formed in asurface of the ceramic substrate and imparting the ceramic substratewith a predetermined rupture strength, the ceramic substrate fracturingalong the at least one laser scribe line during deployment of thedeployable element.
 17. A scribed frangible seal according to claim 16wherein at least one laser scribe line comprises a plurality of laserscribe lines formed in a surface of the ceramic substrate, the pluralityof laser scribe lines defining at least one longitudinally-extendingfault line along which the ceramic substrate fractures when contacted bythe deployable element during deployment thereof.
 18. A scribedfrangible seal according to claim 16 wherein the deployment opening isformed through a structure, and wherein the scribed frangible sealfurther comprises a flexible edge bond adhesively coupling acircumferential portion of the ceramic substrate to the structure.
 19. Amethod for equipping a flight vehicle with a scribed frangible seal, theflight vehicle including a vehicle body configured to house a deployableelement when in a stowed position, the vehicle body having a deploymentopening therein through which at least a portion of the deployableelement passes when moving from the stowed position into a deployedposition, the method comprising: obtaining a scribed frangible seal;positioning the scribed frangible seal over the deployment opening inthe vehicle body at a location at which the scribed frangible seal willbe contacted by the deployable element during deployment thereof; andbonding the scribed frangible seal to the vehicle body to seal thedeployment opening.
 20. A method according to claim 19 wherein the stepof obtaining a scribed frangible seal comprises: laser-scribing aceramic sheet to define a plurality of rigid substrates; breaking theceramic sheet to separate at least one rigid substrate from theplurality of rigid substrates; and laser-scribing an outer face of therigid substrate to yield the scribed frangible seal.